Field of the Invention
The invention relates to a method for inerting a power-producing generator in a power station, in particular a hydrogen-cooled generator.
During operation, generators above a specific rated power are usually cooled through the use of a gaseous coolant. Hydrogen (H.sub.2) has generally proven suitable for that purpose, since it has a lower density, a better thermal conductivity and a higher specific heat than air. Furthermore, the heat capacity of hydrogen can be increased by raising the gas pressure in comparison with air without producing undesirably high gas friction losses in the generator. The gas pressure is therefore generally kept at a level of 3 to 6 bar. The hydrogen is circulated inside a closed cooling circuit of the generator, for example through the use of a multi-stage axial blower.
In order to provide maintenance work which is occasionally required on the generator, or in the event of an emergency, it is necessary to flush or empty the generator and then refill it. In order to avoid highly explosive hydrogen-air mixtures, it is prescribed in absolute terms for those exchange operations (DIN VDE 0530, Part 3) that the generator is to be flushed with an interim or inert gas. In order to do that, in practice carbon dioxide (CO.sub.2) has heretofore been used as the inert gas, as can be seen from the paper entitled "Empfehlungen zur Verbesserung der H.sub.2 --Sicherheit wasserstoffgekuhlter Generatoren" [Recommendations on Improving the H.sub.2 -Safety of Hydrogen-Cooled Generators] 1.sup.st edition 1989, of the "Generators and Motors" working committee of the "Vereinigung Deutscher Elektrizitatswerke" [Association of German Electric Generating Plants]--VDEW, and from the above-mentioned VDE standard.
Patent Abstracts of Japan Publication No. 01 099 452 describes a hydrogen-blow-off device for a generator. A blow-off line for the hydrogen is flushed with argon before the hydrogen is blown-off in order to remove air from the blow-off line. The hydrogen is then removed from the generator through the blow-off line. Since there is no more oxygen in the blow-off line, the hazard of explosion by an oxyhydrogen gas reaction in the blow-off line is eliminated.
Patent Abstracts of Japan Publication No. 58 009 548 describes a device for cooling an electrical rotary machine. A hydrogen tank, an inert gas tank and a pressurized air tank are respectively connected with the rotary machine. U-shaped line segments are provided, which are respectively connected to the feed lines of the three tanks. During operation of the rotary machine the respective line segments for the inert gas tank and for the pressurized air tank are removed and the lines are protected with blind flanges. When the rotary machine is inspected only the U-shaped line segment of the hydrogen tank is removed. An increase in operating safety for operation and maintenance of the rotary machine is achieved through the use of the flange-mountable and dismountable U-shaped line segments.
Filling a hydrogen-cooled generator and prior flushing with CO.sub.2 is likewise described in German Utility Model DE 295 19 578 U1, in German Published, Prosecuted Patent Application DE-S 3644 VIII d/21d1 of Dec. 7, 1943 and in German Published, Non-Prosecuted Patent Application 1 488 079.
Since CO.sub.2 is stored in liquid form in cylinders, a CO.sub.2 -evaporator is necessary to convert it into the gas phase. The evaporator requires additional space and, under certain circumstances, must in turn be provided with a power supply connection for electrical heating to generate the necessary evaporation heat as well as with an emergency power supply. Safety-oriented monitoring of the current CO.sub.2 level can only be realized through the use of a complicated weight measurement of the CO.sub.2 cylinders, since due to the strongly temperature-dependent pressure and the likewise temperature-dependent, simultaneous presence of liquid and gas phases, it is not easily possible to work out the level, for example through the use of pressure.
If, after inerting, it is necessary to gain access to the generator for maintenance purposes, the CO.sub.2 has to be displaced by air in order to avoid toxic hazards.
During that operation, as well as for the above-described inerting operation, the concentrations of inert gas in hydrogen or inert gas in air are usually monitored through the use of CO.sub.2 /H.sub.2 concentration measuring devices.